The present invention refers to high-vacuum pumps, and more particularly it concerns a turbine pump, in particular a turbomolecular pump, comprising a stator stage integrated with a spacer ring and located in correspondence of an intermediate inlet for a gas flowing in counter-current flow to the operating direction of the pump.
Pumps with such an intermediate inlet are employed for example, in leak detectors. In leak detectors a test gas, usually helium, which enters a vessel to be tested or escapes therefrom because of leaks, is led to the intermediate inlet of the pump, then it flows in counter-current flow towards a gas detector, usually a mass spectrometer, connected to the low-pressure side of the pump.
Examples of such pumps are disclosed in U.S. Pat. No. 4,472,962 entitled xe2x80x9cLow Pressure Leak-Detectorxe2x80x9d issued Sep. 25, 1984 and U.S. Pat. No. 5,585,548 entitled xe2x80x9cCounterflow Leak-Detector Unit With A High-Vacuum Pumpxe2x80x9d issued Dec. 17, 1996.
The ""962 patent discloses a pump in which the intermediate inlet opens into an annular channel, formed in the pump housing and surrounding the rotor of an intermediate pumping stage. That pump requires a relatively high vacuum in the area where the test gas enters, a vacuum of the order of 10xe2x88x925 mbar, (1 mPa).
The ""548 patent discloses a pump in which the intermediate inlet opens into a transition chamber separating a group of low-pressure stages and a group of high-pressure stages. The chamber is limited upwards by a rotor impeller and downwards by a stator stage comprising a stationary disc, defining with the rotor shaft a constriction intended for providing a high detection sensitivity without any danger of the pressure in the test gas detector increasing to inadmissible levels. In an embodiment, the disc has a set of axially projecting strips. This pump does not require a relatively high vacuum in the inlet area of the test gas, where it tolerates pressures of the order of 0.1 mbar (10 Pa).
Therefore it is desirable to provide a pump with an intermediate inlet, exhibiting improved performance in terms of compression ratio and conductance of the test gas, such as helium, in order to increase the maximum pressure that can be tolerated at the intermediate port through which the test gas enters.
The present invention provides a pump where the transition chamber is limited by a stator stage integrated with a spacer ring and comprising a disc having a peripheral edge, integral with the disc and forming the spacer ring, and radial blades formed in a peripheral region of the disc and joined therewith at both a radially inner edge and a radially outer edge.